As is known, the cylinder is the main active component of a lock. It is constituted by a stator which is integral with the lock, inside which a rotor can be selectively rotated. The rotor is provided with an opening for the insertion of a coded key. Between rotor and stator, adapted pins are interposed, kept elastically in a position of interference between rotor and stator, of preset length, the coding pattern of the key enabling the alignment of the terminal edge of each pin with the interface surface between stator and rotor, with consequent freedom of rotation of the rotor with respect to the stator.
The coding pattern of the key consists in the provision of a contoured profile thereon which has a progression such that, once the key is completely inserted in the opening of the corresponding rotor, the edge of each pin, pushed by a corresponding portion of the contoured profile of the key in contrast to elastic means, is aligned with the interface surface between rotor and stator.
The main drawback of this type of cylinder is constituted by the need to completely replace the cylinder if a key is lost (or stolen or copied). In fact it is not possible to modify the length of the pins, in order to modify the characteristics of the contoured profile of the key adapted to open the cylinder.
Therefore the replacement of the cylinder is necessary for preventing a malicious person from being able to gain access to the area protected by the lock that is governed by the cylinder by actuating it by means of the key that was found, stolen or copied.
The necessity is therefore obvious of carrying out extremely expensive operations to replace the cylinders whenever a key is lost or stolen or copied.
Particularly innovative cylinders do exist which are supplied directly by the producer with two or more accompanying sets of keys. If one of the keys of one of the sets is lost, it is possible, after subjecting the cylinder to a series of codified and complex operations, to modify its coding pattern thus adapting it to one of the keys of the at least one other set.
The cost of these innovative cylinders is very high and moreover they limit the possibilities of the user since they generally allow only one change of the coding pattern (the cylinder is generally associated with only two sets of keys). Therefore, if a key of the second set is lost (once a first change of coding pattern has been performed) it will be necessary to replace the entire cylinder.